Introduction: Insufficient lesion depth and discontinuity of lesion lines are reasons for reconnections after point-by-point radiofrequency pulmonary vein isolation (PVI).  Different technologies have shown to be useful for prediction of effective lesions. Measurement of the magnitude of local tissue impedance drop (LID) and calculation of lesion size index (LSI) based on monitoring of contact force are examples for corresponding technologies.

Purpose: To compare the acute efficacy of LID guided with LSI guided PVI.

Methods: In this retrospective study we compared two groups of patients who underwent point-by-point radiofrequency PVI for treatment of atrial fibrillation. In the LID-guided group (n=35) energy was delivered using IntellaNav MiFi (Boston Scientific, MA, USA) ablation catheter. Ablation was terminated when LID reached a plateau (Figure A). In the LSI-guided group (n=31) lesions were created using Tacticath (Abbott, MA, USA) ablation catheter until the target LSI was reached in each point (LSI=5 for anterior and LSI=4 for posterior segments respectively, Figure B). The inter-lesion distance of <6 mm with power of 40 W for anterior and 30W for posterior segments was used in both groups. A gap-map and touch-up ablation was performed along the index ablation line if the first pass PVI did not occur, or in the case of an acute reconnection after 20 min of waiting time. In the post hoc analysis initial levels and drop of local and system impedance, average contact force and LSI were included in models predicting PV gaps.

Results: All pulmonary veins were successfully isolated by encirclement of ipsilateral veins with significantly longer median ablation time 30(IQR:27-35) min in LID-guided group as compared to LSI-guided group:25 (IQR:21-31) min (p=0.035). First-pass PVI was achieved in 97 out of 132(73%) circles (LID-guided:43 out of 70 [61%] circles vs LSI-guided:54 out of 62 [87%] circles, p=0.002). Acute reconnections occurred in 14 out of 132 (11%) circles (LID-guided:9 out of 70 [13%] circles vs LSI-guided: 5 out of 62 [8%] circles, p=0.54, Figure C). Overall, significantly more patients had PV gaps when LID-guided ablation was used as compared to LSI-guided (26 out of 35[74%] vs 13 out of 31[42%] respectively, p=0.016). In the post hoc analysis a LID<9.7Ω was the only predictive parameter for PV gap (sensitivity=96.4%, specificity=67%).

Conclusions: LSI-guided ablation resulted in successful PVI with significantly shorter ablation time and fewer PV gaps as compared to LID-guided. This reflects the nature of contact force guided ablation anticipating the quality of catheter-tissue interface before each application, which is not possible with an impedance-only guided approach.

Figure 1. (A): Activation map identified a gap in the right posterior segment after the local impedance drop guided ablation. Examples of the local impedance traces with plateau reached (B): Anatomical map with ablation tags corresponding to calculated lesion size index.

(C): Schematic of antral circumferential area lines with the bar plot representing the rate of the first pass gaps and acute reconnections per segment for the local impedance guided (blue and cyan) and lesion size index guided (red and pink) ablation.